Scientists in Britain say for the majority of Earth's tropical land surface, air passing over extensive forests produces at least twice as much rain as air passing over little vegetation and in some cases forests can increase rainfall thousands of miles away.
"We were surprised to find that this effect occurs strongly across more than half of the tropics," led researcher Dominick Spracklen from the University of Leeds said.
"We found that the Amazon and Congo forests maintain rainfall over the periphery of the forest basins -- regions where large numbers of people live and rely on rainfall for their livelihoods."
Analyzing predictions of future deforestation, the researchers estimated destruction of tropical forests would reduce rain across the Amazon basin by up to a fifth in the dry season by 2050.
"Our study implies that deforestation of the Amazon and Congo forests could have catastrophic consequences for the people living thousands of kilometers away in surrounding countries," Spracklen said.
The findings show the importance of initiatives to protect tropical forests, he said.
The study has been published in the journal Nature.